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4th May 2012, 12:09 PM
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#1 |
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diyAudio Member
Join Date: Sep 2009
Location: Catalonia new Europe state
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6DJ8/ECC88-SRPP Tube Preamplifier
I want to make for a friend one 6DJ8/ECC88-SRPP Tube Preamplifier but I don't have on hand the 150uF, I have 100uF or 220uF, wich one can I use? have I to change the cathode resistor value?
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4th May 2012, 12:10 PM
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#2 |
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diyAudio Member
Join Date: Sep 2009
Location: Catalonia new Europe state
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Ooops forgot the schematic.
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4th May 2012, 12:11 PM
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#3 |
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diyAudio Member
Join Date: Sep 2009
Location: Catalonia new Europe state
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If there is a way to upgrade the schematic your advice will welcome.
Wich value of pot for volume, I have 100K it's ok? Last edited by merlin el mago; 4th May 2012 at 12:16 PM. |
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4th May 2012, 12:16 PM
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#4 |
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diyAudio Moderator
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Either don't use an SRPP or optimize the loading- in a very nice article a few years ago, Merlin Blencowe showed that unlike common-cathode voltage amps, an SRPP will show a distortion null at some (relatively low) value of load. As well, the gain is extremely high for a line amp- he'll probably clip his power amp with the volume control barely advanced.
The schematic has a couple of glaring errors (the input impedance and the bias voltage). You could use a larger cap at the expense of overload recovery time. Or you could substitute a cheap red LED to get near-instantaneous overload recovery, some pretty light, and slightly reduced cost.
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If there's a sucker born every minute, where do the rest of them come from? |
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4th May 2012, 12:34 PM
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#5 |
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diyAudio Member
Join Date: Sep 2009
Location: Catalonia new Europe state
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He has a clone Aleph X of 100W, what's the correct bias voltage?
I have on hand these LEDs: 1.8V 20mA Yellow water clear 1.9V 20mA Red 1.95V 20mA Yellow 2.0V 20mA Green 2.1V 25mA Greed diffused Wich one do you recommend? How can reduce the gain? |
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4th May 2012, 12:46 PM
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#7 | |
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diyAudio Member
Join Date: Sep 2009
Location: Catalonia new Europe state
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Quote:
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4th May 2012, 12:47 PM
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#8 | |
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diyAudio Moderator
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Quote:
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If there's a sucker born every minute, where do the rest of them come from? |
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4th May 2012, 01:00 PM
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#9 |
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diyAudio Member
Join Date: May 2007
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The quoted LF point of 1.6Hz assumes no load (not even a scope probe!). I'm not sure where the input impedance of 240K comes from. The output impedance of 850ohms may be correct (I haven't bothered to do the calculation) but it will only apply above about 2kHz with a small output cap. Everything points to this design being done by someone who is new to audio and so ignorant of details.
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